Copper Schiff base complex as a new immobilized heterogeneous catalyst: experimental, theoretical, biological and docking study

Article abstract of DOI:10.1007/s13738-020-02024-8

Abstract: The novel copper^(II) Schiff base complex was synthesized. Density functional theory calculations at the B3LYP (6-311G**/LANL2DZ) level of theory have been carried out to investigate the structure and geometry of the Schiff base ligand

Full text of DOI:10.1007/s13738-020-02024-8

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-020-02024-8
ORIGINAL PAPER
Copper Schif base complex as a new immobilized heterogeneous
catalyst: experimental, theoretical, biological and docking study
Elham Zarenezhad1 · Sheida Esmaielzadeh2 · Somayeh Behrouz3 · Leila Emami4
Received: 2 May 2020 / Accepted: 29 July 2020
© Iranian Chemical Society 2020
Abstract
The novel copper(II) Schif base complex was synthesized. Density functional theory calculations at the B3LYP (6-311G**/
LANL2DZ) level of theory have been carried out to investigate the structure and geometry of the Schif base ligand and its
copper complex. IR spectra data (experimental and theoretical) show that the ligand Schif base is coordinated to the copper
ion in a bi-negative tetradentate manner with NNOS donor sites. From the theoretical data, it was found that the geometrical
structure of this complex is distorted square planar. In continue, a safe, efcient, and improved procedure for synthesis of
1, 2, 3-triazole derivatives by immobilized [CuL] on silica is described. Terminal alkynes reacted with organic azides in
the presence of a novel copper(I) catalyst, which is prepared by in situ reduction of the copper(II) Schif base complex with
ascorbic acid, in H2O/THF at room temperature. Moreover, immobilized [CuL] on silica was approved to be a chemically
and thermally stable catalyst that can be reused for several times with no signifcant loss in catalytic activity. The in vitro
antifungal activities of title compounds were studied against Candida albicans (ATCC 10231), Candida krusei (ATCC 6258)
and Aspergillus niger (ATCC 16404). Two compounds containing 2-(4-((((diphenylmethylene)amino)oxy)methyl)-1H-1,2,3-
triazol-1-yl)-1-phenylethan-1-one and 2-(4-((((9H-fuoren-9-ylidene)amino)oxy)-methyl)-1H-1,2,3-triazol-1-yl)-1-pheny-
lethan-1-one proved to have potent antifungal activity against Candida albicans and Candida krusei. A molecular docking
study is also discussed for all synthesized compounds. The docking study demonstrated a signifcant interaction between
the two most potent compounds and the active site of Mycobacterium P450DM.
Graphic abstract
Keywords Click reaction · Copper Schif base complex catalyst · Antifungal activities · Molecular docking analysis
Introduction
Heterocyclic compounds containing 1,2,3-triazole structure
have a wide range of applications in biological systems [1].
Among them, 1,2,3-triazole frameworks are potential targets
* Sheida Esmaielzadeh
esmaielzadehsheida@gmail.com
Extended author information available on the last page of the article
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
for drug discovery because of their wide range of biological
activities, such as antiviral, anticancer, anti-HIV, antibiotic,
antibacterial, and antimicrobial [2]. 1, 2, 3 Triazoles are
synthesized by azide-alkyne Click reaction which proposed
for the frst time by Rolf Huisgen in early 1960s, in which a
mixture of 1, 4- and 1, 5-disubstituted 1,2,3- triazoles was
formed [3]. Sharpless and Meldal [4, 5] have developed regi-
oselective synthesis of 1,4-regio isomer in the presence of
Cu(I) catalyst at room temperature, and this reaction became
popular as Click reaction.
Inorganic supports such as silica gels are relatively cheap
and can be used in most organic solvents; also supported
catalysts based on silica gel can be separated from reaction
media by means of simple fltration techniques [20]. Vari-
ous copper(I) sources were used as catalyst such as CuI and
CuOTf. Cu(I) can be in situ produced by using CuSO4∙5H2O
and sodium ascorbate as a reducing agent [21].
Recently, we immobilized homogeneous copper(II) cata-
lyst on solid support which has been employed as reusable
catalysts for regioselective 1,3-dipolar Huisgen cycloaddi-
tion [9]. In this context and in line with our interest in design
and synthesis of new N-heterocycle derivatives [22–25], we
report a new immobilized homogeneous catalyst system on
silica based on Cu [26] and ascorbic acid as reducing agent
for regioselective 1,3-dipolar Huisgen cycloaddition reaction
to access 1,2,3-triazole cores (see Scheme 1).
Catalysis (homogeneous and heterogeneous) plays a
major impact on the chemical industry [6]. The develop-
ment of heterogeneous catalysts for the synthesis of organic
compounds has become a major area of research [7, 8].
Many Schif base metal complexes display brilliant catalytic
activity in various reactions such as Click reaction [9, 10],
oxidation of organic compounds, polymerization reaction,
hydroxylation, aldol condensation, hydrosilylation, epoxida-
tion, reduction of ketones, and Henry reaction in the pres-
ence of moisture. Many Schif base copper complexes have
wide range of applications such as antiproliferative, anti-
infammatory, antiviral, and antimicrobial, properties. They
were useful alternative for preparing various metal catalysts
with diferent applications [11].
Experimental
Materials and methods
General remarks
To improve the recovery and reuse, metal catalyst has
been immobilized onto various supports such as silica gel
[9], activated carbon [12], zeolites [13], amine-functional-
ized polymers [14], amine-functionalized silica [15], and
aluminum oxyhydroxide fber [16]. Also, immobilization of
organometallic complexes on inorganic supports improved
their stability, selectivity and the control of their reactivity
of catalyst [17].
Melting points were determined with an Electrothermal
9100 apparatus. Elemental analyses were performed using a
Heraeus CHN-O-Rapid analyzer. All preliminary chemicals
were purchased from either Fluka or Merck. Solvents were
purifed by standard procedures. Reactions were followed by
TLC using SILG/UV 254 silica-gel plates. Column chroma-
tography was performed on silica gel 60 (0.063–0.200 mm,
70–230 mesh; ASTM). IR Spectra were obtained using a
Shimadzu FT-IR-8300 spectrophotometer. NMR spectra
were recorded on a Bruker Advance DPX-250 (1H NMR
at 250 and 400 MHz and 13C NMR at 62.9 and 100 MHz)
spectrometer in pure deuterated solvents with tetramethyl-
silane as an internal standard. GC/MS were performed on a
Shimadzu GC/MS-QP 1000-EX apparatus (m/z; rel. %). The
There are several procedures to support a homogene-
ous catalyst [18]. One of the most common methods is, to
immobilize them on an insoluble supporting agent to achieve
at so-called heterogenized homogeneous catalyst. The sup-
ports that are used in this approach include inorganic mate-
rials such as silica and organic polymers or alumina [19].
Scheme 1 Synthetic route of Huisgen cycloaddition reaction by the new CuII complexes catalyst
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electronic absorption spectra were measured on PerkinElmer
(LAMBDA 2) double beam. The magnetic susceptibilities
of the copper complexes were carried out on Sherwood
scientifc magnetic susceptibility balance calibrated with
HgCO(NCS)4. Diamagnetic corrections were calculated
from Pascal’s constants. Molar conductance values (1×10−3
M) in DMF solution were determined by means of a Jenway
4310 conductivity meter and a diptype cell with a platinized
electrode at room temperature.
conversion. The catalyst was fltered of, washed with THF/
H2O (5×10 mL), and the fltrate was evaporated under vac-
uum to remove the solvent. The remaining foam was dis-
solved in CHCl3 (100 mL) and subsequently washed with
water (2×100 mL). The organic layer was dried (Na2SO4)
and evaporated. The crude product was purifed by column
chromatography on silica gel and eluted with proper sol-
vents. Characterization data of all synthesized compounds
are described below.
Synthesis of the H2L Schif base ligand
Spectra data for ligand
The Schif base ligand (H2L) was prepared according to the
procedure described in previously published method [22,
27]. The purity of the ligand was evaluated by thin layer
chromatography.
Methyl‑2‑{[3‑(2‑hydroxy‑5‑sodiumsulfitephenyl)methyli‑
dynenitrilo]propyl}amino‑1‑cyclopent‑enedithiocarbox‑
ylate [H2L](5) afforded the product as a yellow solid,
yield: 65%; m.p.: 207 °C; IR (KBr, cm−1): 766 (νC–S),
1152 (νC–S+νC–N), 1263 (νC–O), 1460 (νC=C aromatic), 1631
Preparation of copper (II) complex
(νC=N), 680, 1197 (νS–O, S=O stretching), 2960 (νC–H); 3379
(νO–H); 1H NMR (δ, ppm, 250 MHz, DMSO-d6): 1.26 (3H,
d, J=6.3, Me), 1.75 (2H, m, H4′), 2.39 (3H, s, SCH3), 2.61
(2H, t, J=4.1, H5′), 2.73 (2H, t, J=4.1 H3′), 3.47–3.62 (3H,
m, Hen), 6.77 (1H, d, J=5.2, H3), 7.50 (1H, d, J=5.2, H4),
7.66 (1H, s, H6) 8.62 (1H, s, CH=N), 12.21 (1H, br, NH)
and 13.12 (1H, br, OH); UV–Vis: λmax(DMF, nm): 31 4,
396; MS Spectra: m/z(%) = 437[M + 1]+, 436[M]+, 256,
236, 208, 185, 167, 111, 83, 57; ES-MS m/z; Found (Calc):
C17H21N2O4S3Na, C: 46.48 (46.77); H: 5.06 (4.85); N: 6.68
(6.42); S: 21.79 (22.03%).
(0.23gr, 1 mmol) of H2L Schif base ligand was dissolved in
10 mL methanol/chloroform (1:2, V/V) and (0.19 g, 1 mmol)
of Cu(CH3COO)2. H2O in 10 mL ethanol was added to it.
The resulting mixture was stirred for 24 h. The completion
of the reaction was monitored by using TLC tests. TLC was
performed on silica gel (Merck TLC plate) using appropri-
ate solvent mixture (EtOAc/n-hexan) as eluent. The brown
precipitate that formed was fltered of, washed several times
with H2O to remove unreacted metal ion and dried in air at
room temperature. In spite of all the attempts, preparing of
single crystal of copper (II) complex was unsuccessful.
Spectra data for Copper(II) Complex
Procedure for immobilization of [CuL] on silica
{Methyl‑2‑[3‑(5‑sodiumsulfte‑2‑phenolate)methylidyneni‑
trilo]propyl}aminato(‑1)‑1‑cyclopent‑enedithiocarboxylate
copper (II) [CuL](6) aforded the product as a brown solid,
yield (76%), m.dec.>250 °C; IR (KBr, cm−1): 738 (νC–S),
1110 (νC–S+νC–N), 1254 (νC–O), 1441 (benzene stretch), 1613,
To a solution of [CuL] (0.5 g, 1 mmol) in anhydrous dichlo-
romethane (50 mL), it was added a fresh and active silica
gel (0.6 g, 10 mmol) in 0.063–0.200 mm or 70–230 mesh
size. The suspension solution was stirred for 48 h at room
temperature. Afterward, the suspension solution was fash
fltered (sintered glass) and the solid residue (catalyst) was
washed with anhydrous dichloromethane (2×50 mL). The
catalyst was then dried in a vacuum oven at 60 °C for 4 h and
stored in a refrigerator. Inductively coupled plasma (ICP)
analysis indicated that in each gram of catalyst, there are
0.04 g of active Cu catalyst (0.05 mol%).
1622 (νC=N), 678, 1202 (νS–O, S=O stretching), 2943 (νC–H),
590(νCu–O), 438(νCu–N); UV–Vis: λmax(DMF, nm): 328, 370,
396(sh); ΛM =(10−3M, in DMF, ohm−1 cm2 mol−1): 8.31; µef:
1.79; MS Spectra: m/z (%) = 499[M + 1]+, 498[M]+, 427,
393, 346, 328, 195, 172, 94, 73, 56; ES-MS m/z; Found
(Calc): C17H19N2O4S3NaCu, C: 41.20 (41.00); H: 4.08
(3.84); N: 5.36 (5.62); S: 19.57 (19.31%).
2‑(4‑((((Diphenylmethylene)amino)oxy)methyl)‑1H‑1,2,3‑tri‑
azol‑1‑yl)‑1‑phenylethanone (3a) Column chromatog-
raphy on silica gel (EtOAc/n-hexane = 2:1) aforded the
product as a yellow solid, yield (92%), m.p 182–184 °C; Rf
(EtOAc/n-hexane=2:1, 0.64); IR (KBr, cm−1): 3144, 2922,
1687, 1592, 1462, 1228 cm−1; 1H NMR (δ, ppm, 400 MHz,
CDCl3): δ: 5.52 (s, 2H, CH2–N), 5.75(s, 2H, CH2–O) 7.17–
8.19 (m, 12H, arom, H-triazole), 8.16–8.19 (m, 4H, arom);
13C NMR (δ, ppm, 100 MHz, CDCl3): δ 54.4, 68.02, 118.74,
General procedure for catalytic test
To a round-bottom flask (50 mL) was added a mixture
of alkyne (0.012 mol), catalyst (0.4 g, 0.05 mol%), the
appropriate azide derivative (0.01 mol), and ascorbic acid
(0.1 mol%) in a mixture of THF/H2O (9:1, V/V, 20 mL).
The reaction mixture was stirred at room temperature
until TLC monitoring indicated no further progress in the
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120.70, 124.14, 127.08, 127.26, 128.11, 128.51, 128.96,
130.04, 132.85,133.54, 134.35, 139.29, 140.32, 151.86,
189.18; ES-MS m/z=396 [M+H]. Elemental Anal; Found
(Calc): C24H20N4O2, C: 72.71(73.09); H: 5.08(4. 98); N:
14.13(13.98); O: 8.07 (8.09).
gel (EtOAc/n-hexane = 2:1) aforded the product as a yel-
low product; yield(80%), m.p 195–197 °C; Rf (EtOAc/n-
hexane=2:1, 0.59); IR (KBr, cm−1): 3069, 2860, 1725, 1341
(C=N), 1466, 1263. 1H NMR (δ, ppm, 400 MHz, CDCl3):
5.15 (2H, s, CH2–N), 5.80 (2H, s, CH2–O), 6.71–8.03
(10H, m, arom, H-triazole). 13C NMR (δ, ppm, 100 MHz,
CDCl3): 115.6, 127.1, 127.7, 128.2, 129.8, 131.3, 132.8,
133.7, 156.2, 166.7, 189.0. Elemental Anal.: Found (Calc):
C17H14N3O2Br, C: 54.80 (54.86); H: 3.83 (3.09); N: 11.25
(11.89).
2 ‑ ( 4 ‑ ( ( ( ( 9 H ‑ f l u o r e n ‑ 9 ‑ y l i d e n e ) a m i n o ) o x y )
methyl)‑1H‑1,2,3‑triazol‑1‑yl)‑1‑phenylethanone (3b) Col-
umn chromatography on silica gel (EtOAc/n-hexane=2:1)
aforded the product as a yellow solid, yield (90%) m.p
190–193 °C; Rf (EtOAc/n-hexane = 2:1, 0.63); IR (KBr,
cm−1),: 3150, 2965, 1708, 1535, 1449, 1224 cm−1;1H
NMR (δ, ppm, 400 MHz, CDCl3): δ: 5.30 (s, 2H,CH2–N),
5.78(s, 2H, CH2–O) 7.18–7.92 (m, 14 H, arom, H-triazole;
13C NMR (δ, ppm, 100 MHz, CDCl3): δ: 54.36, 66.54,
115.23, 123.98, 126.36, 127.12, 127.54, 128.16, 132.91,
133.60, 133.84, 134.10, 144.11, 153.33, 160.25, 189.22.
ES-MS m/z=394 [M+H]. Elemental Anal; Found (Calc):
C24H18N4O2, C: 73.08 (72.96); H: 4.60 (4.80); N: 14.20
(14.44); O: 8.11(7.92).
Results and discussion
Initially, we prepared an active catalyst, as is shown in
Scheme 2. Firstly, the unsymmetrical Schif base ligand (5)
was prepared by condensation of the methyl 2-((1-amino-
propan-2-yl)amino)cyclopent-1-ene-1-carbodithioate (4)
and 5-sodiumsulftesalicyl aldehyde in methanol. Compound
(4) was synthesized by published methods [27]. Then, the
resultant yellow powder was recrystallized from methanol/
chloroform 2:1(V/V). The Cu(II) complex (6) was obtained
from addition of (1 mmol) of the appropriate Schif base
ligand (yellow color) in 10 mL of chloroform/methanol 2:1
(V:V), into a solution of 1 mmol of copper acetate in 10 mL
of ethanol. The solution was stirred for 15 min and then
allowed to stand at room temperature for 24 h. After flter-
ing, the brown precipitate was washed several times with
H2O and ethanol and fnally fltered and dried in air at room
temperature. In spite of all the eforts, the copper(II) complex
could not be crystallized.
2‑(4‑(Phenoxymethyl)‑1H‑1,2,3‑triazol‑1‑yl)‑1‑ phenyletha‑
none (3c) Column chromatography on silica gel (EtOAc/n-
hexane = 2:1) aforded the product as a yellow product;
yield: (87%), m.p. 180–182 ℉C; Rf (EtOAc/n-hexane=2:1,
1
0.61); IR (KBr, cm−1): 3059, 2924, 1695, 1669, 1489,
1
1220. H NMR (δ, ppm, 400 MHz, CDCl3): 5.15 (2H, s,
CH2–N), 5.80 (2H, s, CH2–O), 6.80–7.93 (11H, m, arom,
H-triazole). 13C NMR (δ, ppm, 100 MHz, CDCl3): 54.4,
61.1, 112.4, 115.6, 124.9, 127.1, 128.2, 131.3, 132.8, 133.7,
156.3, 168.4, 189.0. ES-MS m/z=394 [M+H]. Elemental
Anal; Found (Calc): C24H18N4O2, C: 73.08 (73.16); H: 4.60
(4.69); N: 14.20(14.42); O: 8.11(7.92).
Theoretical calculation studies of copper(II) complex
1‑(4‑Bromophenyl)‑2‑(4‑(phenoxymethyl)‑1H‑1, 2,3‑tria‑
zol‑1‑yl)ethanone (3d) Column chromatography on silica
By increasing development of theoretical chemistry, DFT
has been extensively used due to their accuracy and low
Scheme 2 Synthesis of Copper(II) Complex
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Fig. 1 Geometry optimized structure of a Schif base ligand, b Cu (II) complex
computational cost to calculate a wide variety of molecular
properties to access reliable results which are in accordance
with experimental values. In present work, the geometry
optimization of the Schif base ligand and its copper com-
plex were performed with the nonlocal gradient corrected
B3LYP density functional with standard 6-311G** basis set
[28] for all elements except Cu and LANL2DZ [29] with
efective core potential for Cu atom, using the Gaussian 03
software package [30].
Table 1 Selected calculated structural parameters of the Schif base
ligand and Cu(II) complex
Band length (Å)
Bond angle (°)
CuL
H2L
CuL
N1–C1
N1–C10
N2–C2
N2–C3
O1–C6
S2–C15
Cu–N1
Cu–N2
Cu–O2
Cu–S2
1.445
1.448
1.447
1.306
1.383
1.648
–
–
–
–
1.443
1.320
1.440
1.316
1.394
1.663
1.947
1.949
1.912
2.127
N1–Cu–N2
N1–Cu–O1
N1–Cu–S2
N2–Cu–O1
N2–Cu–S2
O1–Cu–S2
87.407
175.151
90.716
91.148
174.143
86.217
After optimization the vibrational frequency analyses
were calculated at the same level of theory, with the key-
word freq and pop indicating that the optimized structures
are at the stationary points corresponding to local minimal
without any imaginary frequency. The gas phase optimized
structure of H2L and [CuL] along with labeling atoms is
shown in Fig. 1. The optimized parameters (bond lengths,
bond angles) and some electronic properties such as HOMO
and LUMO energies, chemical hardness and IR data of the
titled compounds were obtained by using the B3LYP/6-
311G**- LAN2DZ method and were discussed in details
(see Tables 1, 2).
Table 2 Calculated quantum chemical descriptors at B3LYP method
with mix basis set
The H2L ligand molecule deprotonates and then acts as a
tetradentate dianionic Schif base ligand framework. It can
be easily seen that the ligand is not planar since the theoreti-
cal dihedral angles between the phenyl ring and cyclopen-
tene ring on the right side of the ligand molecule. The calcu-
lated (N1–C1)(1.445 Å), (N1–C10)(1.448 Å) and (N2–C2)
Complexes
HOMO/eV LUMO/eV Gap/eV Hardness(ꢀ)
H2L1
[CuL(SO3Na)]
[CuL(NO2)] [2] −5.281
−5.453
−5.297
−3.331
−1.702
−1.633
2.099
3.595
3.648
1.049
1.797
1.824
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Journal of the Iranian Chemical Society
(1.447 Å) bond lengths are of the approximate value for a
C–N single bond length, whereas the (N2–C3) (1.306 Å) has
a double bond character which is comparable to the other
C–N single bond values in this molecule. The calculated
(O1–C6) (1.383 Å) and (S2–C15)(1.648 Å) bond distances
are somewhat between the length of a C–O (1.43 Å) [26]
and C–S (1.82 Å) [31] single bond that of a C=O (1.20 Å)
[26] and C=S (1.55 Å) [31] double bond. These values sug-
gest that electron density may be delocalized throughout the
N2–C4–C5 fragment, the aromatic ring and the O1–C10
bond on the right side and N1–C10–C11, cyclopentene
ring and C15–S2 bond on the left side of this ligand. The
Schif base ligand is coordinated to the copper metal core
through the phenolic oxygen atom (O1), the amine nitro-
gen (N1), azomethine nitrogen atom (N2) and thio sulfur
atom (S2). The Cu–N1, Cu–N2, Cu–O1 and Cu–S2 bond
distance in [CuL] is 1.947 Å, 1.949 Å, 1.912 Å and 2.127 Å,
respectively.
Theoretical bond lengths and bond angles for the [CuL]
complex show the copper atom is slightly distorted from the
square planar geometry. For example the calculated angles
obtained for N1–Cu–O1 and N2–Cu–S2 are 175.151° and
174.143°, respectively, instead of 180°.
The agreement between the bond distances and bond
angles results obtained by experimental similar compounds
and theoretical studies is reasonably good [27]. It should
be noted that some observed diferences are most probably
to the X-ray crystal difraction being applied in the solid
phase, while theoretical calculations were carried out in the
gas phase [22].
IR spectra have proven to be the most suitable technique
to give enough information to elucidate the way of bond-
ing of the ligand to the metal ion. In Table 3 we compared
some important normal mode harmonic vibrational wave-
numbers obtained from DFT calculations with those of the
experimentally measured bands of the titled compounds.
The broad and medium band assigned to O–H stretching
vibration of the phenolic OH group appears at 3325 cm−1 in
the [H2L] Schif base ligand spectrum. In the [CuL] complex
the O–H peak disappears. This result indicates that compl-
exation occurred and suggests that the phenolic oxygen atom
is involved in the coordination sphere [32]. The IR multiple
bands at around 2900 in the ligand and its copper complex
are attributed to C-H stretching vibration. The stretching
vibration of C=N observed at 1631 cm−1 of infrared spectra
of Schif base ligand shifted to lower frequency side 1613
and 1622 cm−1 in the spectra of the [CuL] complex indicate
that involvement of azomethine N atom are coordinated to
Cu(II) [33].
The sharp and other band which occurs at 1460 cm−1
and 1441 cm−1 in the free ligand and its Cu complex can
be assigned to the aromatic C=C stretching vibration [34].
The IR spectrum of the free ligand contains strong C–O
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absorption band at 1263 cm−1. This band appeared at
1254 cm−1 in the spectrum of the complex, indicating that
the Schif base ligand coordinates to the metal center through
deprotonated form [35]. A medium to strong intensity band
at 1152 and 766 cm−1 due to ν(CS + CN) and (CS) of the
ligand shifted to lower wavenumber in the [CuL] complex
which indicates the coordination of the thio sulfur atom [22].
Non-ligand band at 560 cm−1 and 438 cm−1 was assigned to
ν(Cu–O) and ν(Cu–N), respectively [36]. The frequencies
characteristics of S–O stretching modes in the IR spectra of
the free ligand were observed around 680 and 1200, respec-
tively. These absorption bands remained almost at the same
position in the [CuL] complex, suggesting that SO3 group is
not involved in coordination [27]. These experimental values
were also in good correlation with computational studies.
Generally, the correlation suggests that the computed struc-
tures are reliable and give credence to conclusions arrived
at from an analysis of the functional density theory. The
small diferences between the calculated and experimental
vibrational wavenumber are likely to originated from (1) the
environmental solvent conditions and (2) the experimental
values are anharmonic frequencies while the calculated val-
ues are aromatic [31].
the [CuL] complex with large hardness and less Eg has more
stability and less chemical reactivity than the ligand and it
is hard molecule.
The comparison of the analysis of molecular orbitals for
the [CuL] complex in this paper and [CuL1] [21] shows that
the Eg of [CuL1] complex is larger than that of the [CuL]
indicating the chemical reactivity of the [CuL1] complex
is decreased and the complex is more stable, so the trend
of catalytic activity was found to be [CuL1]<[CuL]. This
results support the experimental catalytic properties for the
Click reaction which was studied in this work.
Catalytic study
After synthesis and supporting the catalyst on silica gel,
we used this catalyst for the synthesis of some 1,2,3-tria-
zole derivatives. Initially, to obtain the optimized reaction
conditions, we selected the reaction of 2-azido-1-phenyle-
thanone with benzophenone O-prop-2-yn-1-yl oxime as a
model reaction to produce the corresponding 1,2,3-triazole
(3a) (Table 4). This reaction carried out in the presence of
ascorbic acid (0.1 mol%) and [CuL]–SiO2 (0.05 mol%) in
various 2:1 (V/V) organic solvents/H2O at room temperature
(Table 4). As can be seen in Table 4, it is well demonstrated
the solvent has a signifcant role in progress of reaction.
The most appropriate result was obtained when a THF/
H2O mixture was applied (Table 1, entry 5). However, other
mixtures also aforded moderate to good yields of 3a after
longer times (Table 4, entries 1–4, and 6). When H2O was
used alone, the low yield of 3a was attained after 4 h which
is attributed to the lack of solubility of the starting materi-
als in H2O under the examined condition (Table 4, entry 7).
Also, the low yield of 3a was obtained using pure THF after
4 h (Table 4, entry 8).
The frontier orbitals (HOMO and LUMO orbitals) are
very important parameters in quantum chemistry. The difer-
ence energy levels between HOMO and LUMO orbitals [17]
help us to characterize the chemical reactivity and kinetic
stability of the molecule. An electronic system with a larger
Eg should be less reactive than having smaller gap [15, 37].
The HOMO and LUMO energies [17] and contour diagram
of these FMOs (frontier molecular orbitals) of mentioned
ligand and its Cu complex are represented in Table 2 and
Fig. 2. According to Fig. 2, the HOMO electron density
distribution for the Schif base ligand is located over all
cyclopentene ring and N1 atom, and the LUMO level of the
charge density is mostly dominated for benzene ring, N2 and
O1 atoms, while the complex HOMO electron orbitals are
mainly localized on bridging nitrogen atoms, O1 and sulfur
atoms (S1, S2) in ligand and Cu metal atom. The LUMO
includes contributions from both, Cu central atom and other
interacting ligand hetero atoms.
To investigate the optimized amount of [CuL]–SiO2,
diferent amounts of catalyst were examined in the model
reaction (Table 5). As shown in Table 5, the best result was
obtained when 0.05 mol% catalyst was used (Table 5, entry
5). The use of an excess amount of the catalyst has no con-
siderable efect on the progress of the reaction (Table 5,
entries 6 and 7).
The energy gaps (Eg=ELUMO−EHOMO) are found to be
2.099 and 3.595 eV, for the H2L and [CuL] compounds,
respectively. The Eg in H2L is smaller than the [CuL]. As the
Eg decreases the reactivity is increased; so, the free ligand is
more polarized, less stable and more reactive molecule, i.e.,
the electronic charge transfer from the ligand (easily ofer
electrons to an acceptor) to the central metal ion increase.
Other important parameter in quantum chemistry is hard-
ness because the chemical hardness is useful to rationalize
the relative stability and reactivity of chemical compound.
The hardness corresponds to the HOMO and LUMO gap
energy (η=1/2Eg) [38]. On the basis of the data in Table 2
To determine the catalytic potency of [CuL]–SiO2 in the
synthesis of 3a, we tested the model reaction using other Cu
catalysts and compared the results with that of [CuL]–SiO2
(Table 6).
When the reaction was accomplished in the absence of
catalyst, no product was obtained even if the reaction time
was prolonged (Table 6, entry 1). As depicted in Table 6,
shorter reaction time and higher yield of 3a were obtained
using homogeneous and heterogeneous [CuL] (Table 6,
entries 2 and 3) in comparison with other examined copper
catalysts. Previously, we synthesized two new complex of
cu(II) as an efective catalyst. In this study, we compared the
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Journal of the Iranian Chemical Society
Fig. 2 The plot of HOMO (left) and LUMO (right) calculated molecular orbital levels of a H2L and b [CuL]
catalytic efect of new copper complex [CuL] in this study
with [CuL2] and [CuL2] complexes in Ref. [22] (Table 6,
entries 4 and 5). The reaction yield obtained using new cata-
lyst is higher than that of the previous catalysts. Also, the
new catalyst required shorter reaction time in comparison
with that of previous catalyst. NO2 [22] and SO3 substitu-
ents are both an electron withdrawing group. This group
removed electron density from π-system making the Schif
base ligand more electrophilic. The acceptor property of the
Schif base ligand is increased by decreasing the electron
donating properties of the NO2 and SO3 groups; the trend
of the acceptation efect of the Schif base ligand is as fol-
low: H2L–SO3 >H2L–NO2 and therefore leads to decrease
in the kinetic stability of the copper complex i.e., the fol-
lowing trend complex formation of a given Cu cation toward
the Schif base ligand is: ([CuL–NO2] > [CuL–SO3]). So,
the catalytic activity of the ([CuL–NO2] is less than the
[CuL–SO3]). According to the results in Table 6 (entries
2 and 3), both of heterogeneous and homogeneous [CuL]
catalyst are efective, but we applied immobilized [CuL]
on silica as a heterogeneous catalyst, because it has many
advantages such as easy catalyst separation and recovery,
regeneration, and reuse. To prevent the formation of by-
products because of alkyne-alkyne homo-coupling reaction
in the presence of Cu(I) salts, we optimized the stoichiomet-
ric ratio of azide/alkyne which was found to be 1:1.2 for
synthesis of 3a when 0.05 mol% of catalyst was applied.
To assess the scope of this method, we extended the opti-
mized reaction condition to other alkynes and azide cycload-
ditions (Table 7). As the shown in Table 6, [CuL]–SiO2
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Journal of the Iranian Chemical Society
Table 4 Infuence of various miscible organic solvents on conversion of benzophenone O-prop-2-yn-1-yl oxime into 3a using [CuL]–SiO2 at
room temperature
Entry
Solventa
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
H2O/DMSO
H2O/DMF
H2O/t-BuOH
H2O/MeCN
H2O/THF
H2O/acetone
H2O
1.5
1.5
1.5
1.5
1
4
4
80
79
70
60
92
63
39
48
THF
4
aFor entries 1–7, a mixture of 1:2 (V/V) solvents were used
bIsolated yield
Table 5 Infuence of diferent amounts of catalyst on conversion of benzophenone O-prop-2-yn-1-yl oxime into 3a at room temperature
Entry
[CuL]–SiO2 (mol%)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
0.01
0.02
0.03
0.04
0.05
0.06
0.07
4
3
3
2
1
1
1
40
52
60
65
92
92
92
aIsolated yield
proved to be efective catalyst for Huisgen cycloaddition
between diferent α-azido ketones and alkynes. The struc-
tures of all synthesized compounds 3a–3d were character-
ized by IR, 1H NMR and 13C NMR, and elemental analyses.
(ATCC 6258) and Aspergillus niger (ATCC 16404). The
minimal inhibitory concentrations (MICs) of the tested
compounds were determined by the micro-broth dilution
method in 96-well microplates according to the CLSI-
M27-A3 [39]. The specified amount of triazole com-
pounds was dissolved in DMSO and serially diluted in
the standard RPMI-1640 medium (Sigma Chemical Co.)
bicarbonate (maximum concentration was considered
512 μg/mL for all compounds). Briefy, the inoculum sus-
pension was added to each well and incubated at 35 °C.
Antifungal studies
The in vitro antifungal activity of 1,2,3-triazol molecules
3a–3d was assessed against some pathogenic fungi com-
prising Candida albicans (ATCC 10231), Candida krusei
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Journal of the Iranian Chemical Society
Table 6 Comparison of our previous copper catalysts with [CuL]–SiO2 for preparation of 3a
Entry ref
Catalyst
Time (h)
Yielda (%)
1
2
3
–
5
1
1
2
2
0
92
92
74
88
Hetero b
Homo c
[CuL1]
[CuL2]
4 [22]
5 [22]
aIsolated yield
bHeterogeneous [CuL]
cHomogeneous [CuL]
Table 7 ‘Click’ cycloaddition of azides with alkynes
alkyl
halid
182–184
190–193
180–183
195–197
All susceptibility testing was performed in duplicate. Flu-
conazole (FLZ) was chosen as the reference drug. As the
MIC values indicate (Table 8), 3a was the most potent
agents against all tested fungal species; also 3b showed
antifungal activity.
Molecular docking studies
Molecular docking simulation of all synthesized com-
pounds (3a–3d and fuconazole) was done to investigate
the possible interaction and free binding energy (kcal.
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Journal of the Iranian Chemical Society
Table 8 In vitro antifungal profles of 3a–3d
carbonyl group between 1, 2, 3 triazole and phenyl ring is
involved in hydrogen bond interaction with residue Ala 256
at distance 3.47 Å in compound 3d.
Compound
MICa (µg/ml)
Candida
albicans
Candida krusei
Aspergil-
lus niger
Docking study
3a
32
64
128
256
0.25
64
64
128
128
64
128
128
256
128
2
3b
The X-ray crystallographic structure of cytochrome P450
14α-demethylase (PDB ID: 1EA1) was obtained from Pro-
tein Data Bank (PDB data base; http://www.rcsb.org), and
converted to PDBQT using the MGLTOOLS 1.5.6 [42].
The chemical structures of the tested compounds were
drawn and optimized by the ChemBioDraw (version 12.0)
and HyperChem Professional Version 8 (Hypercube Inc.,
Gainesville, FL, USA).
3c
3d
Fluconazoleb
Examined fungi: Candida albicans (ATCC 10231), Candida krusei
(ATCC 6258) and Aspergillus niger (ATCC 16404)
aMinimal inhibitory concentration
bReference drugs for fungal species
AutoDock Tools 1.5.4 program was used for all the pre-
processing steps for receptor structure, and tested ligands
were performed (8) (The Scripps Research Institute, La
Jolla, California, USA) [43]. The co-crystal ligand was
redocked, to verify the validation of docking calculations,
and the fnal docked conformations resulted in 1–1.5 Å root-
mean-square deviation. The Lamarckian genetic algorithm
(LGA) was applied to model the interaction between ligands
and 14α-demethylase active site. For the Lamarckian genetic
algorithm: 27,000 maximum generations; a gene mutation
rate of 0.02 and a crossover rate of 0.8 were applied. The
grid box size was set to 40 × 40 × 40 points in x, y and z
directions, respectively. The box was centered based on the
co-crystal ligand with a spacing of 0.375 Å. Cluster analysis
was performed on the docked results using an RMSD (root-
mean-square deviation) tolerance of 2 Å. All interactions
were visualized and evaluated on the basis of docking results
by VMD software [44].
Table 9 The bonding energies (kcal mol−1) of the tested compounds
using AutoDock Vina
Compounds
Binding energy (Kcal mol−1
)
Log P
for 1EA1
3a
−11.9
−11.4
−9.8
−9.7
4.91
4.55
2.93
3.75
0.99
3b
3c
3d
CO-crystal ligand
−8.9 (fuconazole)
mol−1) of ligand-complex into the active site of lanosterol
14α-demethylase enzyme (1EA1). All the docking protocols
were done on validated structures, with RMSD values below
2 Å. The range of binding energy was seen between −11.9
(Kcal mol−1) to − 9.7 (Kcal mol−1). Fluconazole binding
energy was observed at −8.9 (Kcal mol−1) (Table 9).
All the tested compounds showed high docking binding
energies than the co-crystal ligands (fuconazole), and the
compounds 3a, 3b had the best binding energy values as well
as highest antifungal activity. The good biological activity of
compounds 3a, 3b can be described to their strong binding
afnity with lanosterol 14α-demethylase enzyme. This may
be caused better hydrophobic and van der Walls interactions
between diphenyl and fuorene moiety of 3a and 3b com-
pounds with Fe2+ in the heme molecule of 14α-demethylase.
On the other hand, it seems to be related to the ratio of their
lipophilicity and electronegativity. It should be noted that
suitable hydrophilicity/lipophilicity balance can enhance the
penetration to fungal cells [40, 41]. As it is shown in Fig. 3,
pi–pi bond interaction exists between 1, 2, 3 triazole group
of 3a, 3b and Tyr 76. There is also existed a pi-hydrogen
bond interaction between phenyl groups of diphenyl oxime
of 3a with Ala 256 at distance 3.99 Å. Compound 3c has
hydrogen bond interaction between 1,2, 3 triazole groups
with Arg 96 at distance 3.27 Å. As depicted in Fig. 3, the
Conclusions
Synthesis and characterization of Schif base ligand and its
CuII complex were described. Then, the computational study
allows us to obtain optimized structure, molecular param-
eters, HOMO, LUMO, and HOMO–LUMO band gap, IR
vibrational frequencies, characteristics of new tetradentate
copper complex. Immobilized [CuL] on silica as a new and
convenient heterogeneous catalyst was demonstrated to be
an efcient, thermally and chemically stable, environmental
compatible and low-cost catalyst that can be easily prepared
and reused for many consecutive runs without a signifcant
decrease in its catalytic reactivity. The catalytic study has
shown a simple, one-pot reaction between terminal alkynes
and organic azides in the presence of [CuL]–SiO2, which
gave very good to excellent yields of medicinally impor-
tant nitrogen heterocycles. The advantages of the reported
method are short reaction time, simple method and high
yields. The antifungal tests have shown antifungal activity
1 3

Journal of the Iranian Chemical Society
Fig. 3 Interactions of 3a, 3b, 3c and 3d with the residues in the binding site of 1EA1 receptor
2. D. Dheer, V. Singh, R. Shankar, Bioorg. Chem. 1, 71 (2017)
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demonstrated the appropriate ftting of 3a and 3b in active
site of Mycobacterium P450DM enzyme.
5. C.W. Tornøe, C. Christensen, M. Meldal, J. Org. Chem. 67, 9
(2002)
Acknowledgements This study was supported by Fasa University of
Medical Sciences and Islamic Azad University, Darab Branch.
6. E. Farnetti, R. Di Monte, J. Kašpar, in Inorganic and Bio-Inor-
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Compliance with ethical standards
8. H.G. Hosseini, E. Doustkhah, M.V. Kirillova, S. Rostamnia, G.
Mahmoudi, A.M. Kirillo, Appl Catal. A Gen. 25, 96 (2017)
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Farjam, J. Iran. Chem. Soc. 14, 2 (2017)
Conflict of interest The authors declare that they have no confict of
interest.
10. M.N. SoltaniRad, S. Behrouz, J. Mohammadtaghi-Nezhad, E.
Zarenezhad, M. Agholi, Appl. Organomet. Chem. 33, 4 (2019)
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Afliations
Elham Zarenezhad1 · Sheida Esmaielzadeh2 · Somayeh Behrouz3 · Leila Emami4
1
3
Noncommunicable Diseases Research Center, Fasa
Medicinal Chemistry Research Laboratory, Department
of Chemistry, Shiraz University of Technology,
Shiraz 71555-313, Iran
University of Medical Sciences, Fasa, Iran
2
Department of Chemistry, Darab Branch, Islamic Azad
University, Darab, Islamic Republic of Iran
4
Faculty of Pharmacy, Shiraz University of Medical Sciences,
Shiraz, Islamic Republic of Iran
1 3